1. Field of the Invention
The present invention relates to a vacuum deposition apparatus which can form a deposited film having a decreased number of surface defects attributed to dust particles, molecular clusters, and the like. While the concept of the present invention is applicable to all types of vacuum deposition apparatuses, description will be made of a molecular beam epitaxial growth apparatus as a representative one of those vacuum deposition apparatuses.
In order to effect molecular beam epitaxial growth (representative of vacuum deposition) with as small a number of surface defects as possible, the purity of a material for crystal growth to be used in a molecular beam source (representative of various primary evaporation sources) is raised, and/or an oil free pumping system capable of raising the degree of cleanness inside a molecular beam epitaxial growth chamber is used to create a super high vacuum wherein molecular beam epitaxial growth is effected.
In a molecular beam epitaxial growth apparatus wherein the above-mentioned conventional techniques are utilized, however, dust particles, molecular clusters (large bunches of molecules, which may often be formed and fly as such without being divided into individual molecules when a molecular beam is formed by vacuum evaporation), and the like in a space in a molecular beam epitaxial growth chamber cannot be removed therefrom, even though impurities in a gas itself remaining in the chamber space and in a material for crystal growth can be removed.
In general, dust particles and the like are not easy to remove from an apparatus wherein a super high vacuum is maintained. Therefore molecular beam epitaxial growth, using such an apparatus, involves a defect of being accompanied by development of a considerably large number of surface defects attributed to dust particles and molecular clusters. Particularly where a molecular beam source as a primary evaporation source (evaporation source to be used for film formation) is combined with another molecular beam source as a secondary evaporation source (evaporation source to be used for doping) between which and a substrate a DC voltage is applied to increase the efficiency of doping with an impurity or dopant contributory to electric conduction through a crystalline (single crystal or polycrystalline) film to be formed, the number of surface defects in the film tends to notably increase. Thus, a measure against such a tendency has been in serious demand.